1. Field of the Invention
The invention is directed to an improvement in the driving of mixing tools used in the preparation of granular, pulverulent, liquid or pasty materials; a specific example is the mixing of polyvinyl chlorides. Present prior art workers generally utilize a vertical cylindrical mixing vessel having a vertically mounted power shaft mounted therein and supporting upper and lower mixing blades. The action of these blades produces both a mixing and a heating condition. It has heretofore been the practice to employ a variable speed, or two-speed, drive so as to regulate mixing in accordance with the increase or decrease in the power requirements as the mixing cycle progresses.
2. Description of the Prior Art
A preliminary patentability search was conducted in the United States Patent Office in an effort to develop those United States Patents disclosing mixing arrangements closest to that shown and claimed herein. No assertion is made, however, that the best art was developed by such search although that was indeed the purpose thereof. The United States Patents developed by that search are U.S. Pat. Nos.: 1,682,735; 1,925,152; 1,997,035; 2,015,244; 2,118,500; 2,668,694; 2,682,810; 2,721,062; 2,778,614; 2,784,950; 2,972,168; 3,194,504; 3,352,543; and 3,578,876.
U.S. Pat. No. 1,682,735 is an early reference illustrating separately driven concentric shafts. U.S. Pat. No. 1,925,152 illustrates apparatus for mixing ice cream and the like, again involving concentric shafts.
U.S. Pat. No. 1,997,035 also relates to an ice cream making device. Scrapers and beaters are mounted on concentric shafts. The scrapers are directly powered by an electric motor and the beaters may be engaged or disengaged with the same electric motor by clutch means so that the scrapers may operate during the preliminary chilling time and the beaters may be operated thereafter.
U.S. Pat. No. 2,015,244 illustrates a mixer for slaking lime having two hand-powered concentric shafts. U.S. Pat. No. 2,118,500 illustrates a mixer for "plastic" material such as bakery dough. Beaters, mounted on concentric shafts, may be driven at differential speeds or in unison; this is accomplished through the use of separate motors or of a single motor through variable speed drives which may be manually adjusted.
U.S. Pat. No. 2,668,694 illustrates a vertical, cylindrical mixing chamber provided with concentric shafts extending downwardly thereinto. The inner shaft is driven by motor 48 and the outer shaft is driven by motor 54 at different speeds to provide improved mixing.
U.S. Pat. No. 2,682,810 teaches a pulper having a large diameter, slow moving disc 40 to provide circulation, the disc 40 being attached to a shaft 42 driven by motor 48. A fast moving disc 30 is adapted to provide the defibering action and is carried on shaft 32 driven by motor 34. The shafts are concentric and are driven at different speeds.
U.S. Pat. No. 2,721,062 teaches a butter making device, again having concentric shafts driven at different speeds by separate hydraulic engines 42 and 45.
U.S. Pat. No. 2,778,614 illustrates a mixer having concentric shafts driven by a single motor. The shafts are intended not only to rotate at different speeds, but also in opposite directions. U.S. Pat. No. 2,784,950 describes a mixing machine for chopped meats and the like, a single motor again driving two concentric shafts at different speeds and in different directions. U.S. Pat. No. 2,972,168 relates to a mixing and extruding device utilizing concentric shafts, one shaft driving the other.
U.S. Pat. No. 3,194,504 is of interest in that it illustrates concentric shafts driven by separate motors mounted at either end of the mixing chamber. U.S. Pat. No. 3,352,543 illustrates separate mixing means which may be mounted on concentric shafts so as to be turned in the same or opposite directions at the same or different speeds. Again, however, two separate, variable speed motors are contemplated. Similarly, U.S. Pat. No. 3,578,876 illustrates a mixer having concentric shafts which may be coupled or uncoupled, again however more than one motor being required.